BRUSSELS: European Union leaders on Friday reached a deal on how to help developing nations tackle climate change, but without putting a figure to Europe's contribution, officials said.

"We have an agreement," said Swedish Prime Minister Fredrik Reinfeldt, at the end of a two-day European summit in Brussels.

"The EU now has a strong negotiating position and the countdown to Copenhagen now has started," he added, referring to international climate talks in Denmark in December.

The EU leaders agreed that developing nations would need 100 billion euros (150 billion dollars) worth of help annually by 2020 to tackle climate change and to deal with its consequences.

However, the EU leaders failed to say how much of that money would be coming from Europe, amid strong differences mainly between the poor eastern European nations and the richer west.

Lithuanian President Dalia Grybauskaite said that a working group would now be set up to seek a concrete formula on how the bill is divided up in Europe.

Lithuania, Poland and seven other eastern EU nations have been firmly against the idea of linking contributions to polluting levels, which would leave them with a heavy bill.

They instead suggested that the burden sharing be divided according to national income, which would put the onus very much on the richer western European nations.

The 27-nation bloc prides itself on leading the fight against climate change, and has already agreed to cut greenhouse gas emissions by 20 percent by 2020, but many fear its leadership role could be compromised if it didn't come to the Copenhagen talks with a strong, unified approach.

Otherwise Europe's voice will be weakened when trying to persuade the likes of China, the United States and India to make swingeing cuts themselves.

The EU has also said it is willing to increase its own promised emissions cuts to 30 percent if the rest of the developed world does likewise at Copenhagen.

"We can now look the rest of the world in the eyes and say we Europeans have done our job," said EU Commission chief Jose Manuel Barroso at the summit-closing press conference.

"It was essential that the European Union kept its leadership role and we have done that," he added.

However, he cautioned that the EU "offers are not a blank cheque... we are ready to act if our partners are ready to deliver."

The decision by the European leaders not to publish their own contributions to the 100-billion-euro pot ahead of the UN climate talks was not welcomed by environmentalists.

The Greens in the European parliament dismissed the deal as "a calamitous result for the climate," accusing the 27 heads of state and government of refusing to put their hands in their pockets.

Seven central and eastern European Union members, led by Poland, had also sought to have more concrete proposals on how Europe is to share the bill for Copenhagen.

They are concerned that if national contributions are decided by polluting levels rather than on gross national income levels they will be unfairly hit.

"You have a number of members states, the largest ones, that are against putting on the table a concrete offer from the European Union," Polish EU affairs minister Mikolaj Dowgielewicz told reporters on the sidelines of the summit.

"What the nine (eastern) nations are looking for is a fair burden sharing inside the union.

"We don't think you can make an assumption that Bulgaria or Romania will pay more than Denmark or the Netherlands because it would be purely absurd."

Europe's overall goal is to limit global warming to no more than two degrees Celsius from pre-industrial levels.

On Thursday, the first day of the summit, EU leaders cleared a major obstacle holding up the massive Lisbon reform treaty, paving the way for a new-look EU with its first-ever president. Related article: Support fading for Blair as EU president.

At talks in Brussels, the leaders approved a proposal to satisfy a last-minute demand by the deeply eurosceptic Czech President Vaclav Klaus for his country to win an opt-out from the EU's charter of fundamental rights.